Reactivity trends of cobalt(III) complexes towards various amino acids based on the properties of the amino acid alkyl chains

The reactivity of the cobalt(III) complexes dichlorido[tris(2-aminoethyl)amine]cobalt(III) chloride, [CoCl2(tren)]Cl, and dichlorido(triethylenetetramine)cobalt(III) chloride, [CoCl2(trien)]Cl, towards different amino acids (l-proline, l-asparagine, l-histidine and l-aspartic acid) was explored in detail. This study presents the crystal structures of three amino acidate cobalt(III) complexes, namely, (l-prolinato-κ2 N,O)[tris(2-aminoethyl)amine-κ4 N,N,N,N]cobalt(III) diiodide monohydrate, [Co(C5H8NO2)(C6H18N4)]I2·H2O, I, (l-asparaginato-κ2 N,O)[tris(2-aminoethyl)amine-κ4 N,N,N,N]cobalt(III) chloride perchlorate, [Co(C4H7N2O3)(C6H18N4)](Cl)(ClO4), II, and (l-prolinato-κ2 N,O)(triethylenetetramine-κ4 N,N,N,N)cobalt(III) chloride perchlorate, [Co(C4H7N2O3)(C6H18N4)](Cl)(ClO4), V. The syntheses of the complexes were followed by characterization using UV-Vis spectroscopy of the reaction mixtures and the initial rates of reaction were obtained by calculating the slopes of absorbance versus time plots. The initial rates suggest a stronger reactivity and hence greater affinity of the cobalt(III) complexes towards basic amino acids. The biocompatibility of the complexes was also assessed by evaluating the cytotoxicity of the complexes on cultured normal human fibroblast cells (WS1) in vitro. The compounds were found to be nontoxic after 24 h of incubation at concentrations up to 25 mM.